Managing Recording 'Takes'
When you make a recording it goes into your Project's recording folder.  By default, a recording is named based on the track's name.

Recordings are deleted when you save your project or quit the software if the recording was not included in a project that you saved. 

So, if you make a recording and aren't happy with it, simply click Undo on the toolbar or delete it by clicking the Delete key or selecting Delete from the Edit menu.  If you are worried about filling up your hard drive with bad takes, simply delete the take from within Mixcraft and then Save your project.